Sandpaper with non-slip coating layer

ABSTRACT

The present disclosure generally relates to abrasive articles for abrading a work surface such as, for example, flexible sheet-like abrasive articles, as well as methods of making and using such abrasive articles. Some embodiments of the abrasive articles include an improved, more heat resistant non-slip coating or layer.

TECHNICAL FIELD

The present disclosure generally relates to abrasive articles forabrading a work surface such as, for example, flexible sheet-likeabrasive articles, as well as methods of making and using such abrasivearticles.

BACKGROUND

Sheet-like abrasive articles are commonly used in a variety of sandingoperations including, for example, hand sanding of wooden surfaces. Inhand sanding, the user holds the abrasive article directly in his or herhand and moves the abrasive article across the work surface. Sanding byhand can, of course, be an arduous task.

Sheet-like abrasive articles include, for example, conventionalsandpaper. Conventional sandpaper is typically produced by affixingabrasive material to a relatively thin, generally non-extensible,non-resilient, non-porous backing (e.g., paper). The thin, flat,slippery nature of conventional sandpaper backing materials makesconventional sandpaper difficult to grasp, hold, and maneuver. Becauseof the slippery nature of conventional sandpaper, to hold a sheet ofsandpaper securely, a user will grasp the sheet of sandpaper between hisor her thumb and one or more of his or her remaining fingers. Holdingthe sandpaper in this manner is uncomfortable, can lead to muscle crampsand fatigue, and is difficult to maintain for an extended period oftime. In addition, the thumb is typically in contact with the abrasivesurface of the sandpaper, which can irritate or damage the skin. Also,because the thumb is positioned between the sandpaper and the worksurface, grasping the sandpaper in this manner interferes with thesanding operation. That is, due to the position of the thumb, a portionof the sandpaper abrasive surface is lifted away from the work surfaceduring sanding. Because the lifted portion is not in contact with thework surface, the full sanding surface of the sandpaper is not utilized,and the effectiveness of the sandpaper is, therefore, diminished.

During hand sanding, a user often applies pressure to the sandpaperusing his or her fingertips. Because of the thin nature of the backingmaterials used in conventional sandpaper, the finger pressure isconcentrated in the regions where the finger pressure is applied. This,in turn, causes the sandpaper to wear and/or load unevenly, and canproduce an uneven sanding pattern on the work surface.

Some sandpaper can be used in either wet or dry environments. In wetenvironments, common applications include filler sanding, putty sanding,primer sanding and paint finishing. A particular problem encounteredwith certain sandpaper in wet environments is the tendency forsheet-like article to curl. Curling of the abrasive article can be asignificant nuisance to the user. A similar effect can also occur whenabrasive articles are stored in humid environments. To mitigate curling,abrasive sheets are sometimes preflexed in the manufacturing process,but this is generally ineffective in preventing curling during use.

Conventional sandpaper is typically sold in standard size sheets, suchas 9×11 inch sheets. To make sandpaper easier to use, users often foldthe sandpaper, thereby producing smaller sheets that are easier tohandle. Folding the sandpaper, however, produces a jagged edge, and alsoweakens the sandpaper along the fold line. During the rigors of sanding,the weakened fold line may tear, thereby resulting in premature failureof the sandpaper.

To resolve at least some of the above-identified concerns, 3M Companydeveloped sandpaper that has a non-slip surface. Such sandpaper isdescribed in, for example, U.S. Pat. No. 8,662,962. The commercialproduct, 3M No-Slip Grip™ Advanced Sandpaper, provides at least some ofthe following advantages: improved handling, ease of use, comfortableuse, relatively easy and inexpensive to manufacture, improved cut,improved durability, and produces finer scratches than a comparablesheet of sandpaper.

SUMMARY

The inventors of the present disclosure learned that some users placesheets of sandpaper (or portions thereof) on power sanding tools. Insome instances of high-speed use on power tools, the non-slip coating onthe sandpaper can soften or melt, sticking to the power tool. Theinventors of the present disclosure sought to formulate an improvedno-slip grip coating that provides added heat resistance withoutsignificantly compromising the advantages of the existing non-slipsandpaper.

The present disclosure provides a sheet of sandpaper comprising (1) abacking layer having opposed first and second major surfaces, (2) anadhesive make coat directly on the first major surface, (3) abrasiveparticles at least partially embedded in the make coat, thereby definingan abrasive surface, and (4) a non-slip layer on the second majorsurface, the non-slip layer comprising (a) a dimer acid polyamide, (b)an elastomer, and (c) a tackifying agent.

Advantageously, this configuration provides a coated abrasive thatdisplays superior curl-resistance and improved overall cut and finishperformance as compared with prior art abrasive articles.

BRIEF DESCRIPTION OF DRAWINGS

The present disclosure will be further described with reference to theaccompanying drawings, in which:

FIG. 1 is a cross sectional view of a sheet of sandpaper according tothe disclosure;

FIG. 2 is a perspective view of a second embodiment of the disclosure;and

FIG. 3 is a photograph of various Examples during a Wet Curl test.

Layers in certain depicted embodiments are for illustrative purposesonly and are not intended to absolutely define the thickness, relativeor otherwise, or the location of any component. While theabove-identified figures set forth several embodiments of thedisclosure, other embodiments are also contemplated, as noted in thediscussion. In all cases, this disclosure presents the disclosure by wayof representation and not limitation. It should be understood thatnumerous other modifications and embodiments can be devised by thoseskilled in the art, which fall within the scope and spirit of theprinciples of the invention.

DETAILED DESCRIPTION

Referring now to the drawings, FIG. 1 shows a cross-section of asheet-like abrasive article 10, such as a sheet of sandpaper, comprisinga flexible backing layer 12 having opposed first 12 a and second 12 bmajor surfaces, a flexible non-slip coating layer 14 on the backinglayer first major surface 12 a, an adhesive make coat layer 16 on thebacking layer second major surface 12 b, and a plurality of abrasiveparticles 18 at least partially embedded in the make coat layer 16. Theabrasive article 10 may be provided in, for example, a stack ofindividual sheets, or in roll form, wherein the abrasive article 10 mayhave an indefinite length.

As used herein, the expression “sheet-like” refers generally to thebroad, thin, flexible nature of the abrasive article 10. As used herein,the expression “coating” refers generally to at least a single layer ofgenerally flowable material, such as a liquid or a solid powder that canbe applied directly to a surface. A coating, therefore, does not includea separate sheet of material laminated to a surface. As used herein, theexpression “layer” refers generally to the non-slip material forming adiscrete stratum on top of the backing layer 12 (i.e., the non-slipmaterial does not soak through the entire thickness of the backing layer12).

In one end use application of the disclosure, the sheet-like abrasivearticle 10 may be used for hand sanding a work surface, such as a woodensurface or work piece. That is, the abrasive article 10 may be used toremove material from a surface by contacting the abrasive article 10directly with one's hand (i.e., without the aid of a tool, such as asanding block) via the non-slip coating layer 14, and subsequentlymoving the abrasive article 10 against the work surface. It will berecognized that the present disclosure may also be used withmanually-operated sanding tools and sanding blocks, or with power tools.

The backing layer 12, the non-slip coating layer 14, the adhesive makecoat layer 16, and the abrasive particles 18 are each described indetail below.

Backing 12

Suitable materials for the backing layer 12 include any of the materialscommonly used to make sandpaper including, for example, paper, cloths(cotton, polyester, rayon) polymeric films such as thermoplastic films,foams, and laminates thereof. The backing layer 12 will have sufficientstrength for handling during processing, sufficient strength to be usedfor the intended end use application, and the ability to have thenon-slip coating 14 and make coat 16 applied to at least one of itsmajor surfaces.

In some embodiments, the backing layer 12 is formed of paper. In someembodiments, paper is a desirable material for the backing layer 12because it is readily available and is typically low in cost. Paperbackings are available in various weights, which are usually designatedusing letters ranging from “A” to “F”. The letter “A” is used todesignate the lightest weight papers, and the letter “F” is used todesignate the heaviest weight papers. As explained more fully below, thepresent disclosure allows any weight paper to be used withoutexperiencing the drawbacks associated with conventional sandpaperbackings noted above.

In the illustrated embodiment, the backing layer 12 is continuous. Thatis, the backing layer 12 does not contain holes, openings, slits, voids,or channels extending there through in the Z-direction (i.e., thethickness or height dimension) that are larger than the randomly formedspaces between the material itself when it is made. The backing may alsocontain openings (i.e., be perforated), or contain slits. In someembodiments, the backing layer 12 is generally non-extensible. As usedherein, the term “non-extensible” refers to a material having anelongation at break of no greater than about 25%. In some embodiments,the material has an elongation at break of no greater than about 10%. Insome embodiments, the material has an elongation at break of no greaterthan about 5%.

In certain embodiments, such as when the backing layer 12 is formed ofpaper, the backing layer 12 may be relatively thin, and typically has athickness of no greater than about 1.5 mm, no greater than about 1 mm,or no greater than about 0.75 mm. In such embodiments, the backing layer12 is generally not resilient. The backing layer 12 may also be porousor non-porous. In another embodiment, such as when the backing is a foammaterial, the backing layer may be somewhat thicker. For example, inembodiments having a foam backing layer, the backing layer may have athickness of at least about 2 mm, at least about 5 mm, or at least about10 mm.

The backing layer 12 may also be formed of a cloth material or film,such as a polymeric film. Cloth materials are desirable because they aregenerally tear resistant and are generally more durable than paper andfilm materials. In addition, cloth backings tolerate repeated bendingand flexing during use. Cloth backings are generally formed of wovencotton or synthetic yarns that are treated to make them suitable for useas a coated abrasive backing. As is the case with paper backings, clothbackings are available in various weights, which are usually designatedusing a letter ranging from “J” to “M” with the letter “J” designatingthe lightest weight cloth, and the letter “M” designating the heaviestweight cloths.

Suitable film materials for the backing layer 12 include polymericfilms, including primed films, such as polyolefin film (e.g.,polypropylene including biaxially oriented polypropylene, polyesterfilm, polyamide film, cellulose ester film). In one suitableimplementation of the present disclosure, the backing layer 12 includesa polyurethane, such as those described in US Publication No.2017/0043450 (Graham et al.), including at least one thermoplasticpolyurethane (TPU). In some embodiments, the backing may comprise asingle thermoplastic polyurethane or a combination of thermoplasticpolyurethanes. One suitable class of polyurethanes is aromaticpolyether-based polyurethanes, particularly thermoplasticpolyether-based polyurethanes. In some embodiments, the thermoplasticpolyether-bases polyurethanes are derived from4,4′-methylenedicyclohexyl diisocyanate (MDI), a polyether polyol, andbutanediol.

Non-Slip Coating Layer 14

In some embodiments, the sandpaper 10 includes a non-slip coating layer14, which defines a non-slip, or slip resistant, outer surface 14 a ofthe sandpaper 10. “Non-slip” or “slip resistant” coatings, layers, ormaterials refer to coatings, layers, or materials that tend to increasethe coefficient of friction of the backing layer surface to which thenon-slip material is applied. That is, if the surface of the backinglayer 12 a to which a non-slip coating layer is applied has acoefficient of friction of “x” prior to when the coating is applied, andthe coating—as applied to the surface of the backing—provides a surfacethat has a coefficient of friction that is greater than “x”, then thecoating is a “non-slip” coating. Or stated another way, if the coatingtends to increase the coefficient of friction of the backing surface towhich it is applied, then the coating qualifies as a “non-slip” coating.

In one embodiment, the non-slip coating layer 14 has an average peakstatic coefficient of friction of at about 1 gram, at least about 1.25grams, or at least about 1.5 grams when measured according to ASTM D1894-08 (Standard Test Method for Static and Kinetic Coefficients ofFriction of Plastic Film and Sheeting) at 23° C. using an IMASSslip/peel tester (SP2000, commercially available from InstrumentorsInc., Strongsville, Ohio), and/or an average kinetic coefficient offriction of at least about 0.75 grams, at least about 1 gram, or atleast about 1.25 grams

The non-slip coating layer 14 is provided on the first major surface 12a of the backing layer 12 opposite the make coat 16 and abrasiveparticles 18. The non-slip coating layer 14 outer surface 14 a may haveno tack, or have a low level of tackiness. Tack or tackiness as usedherein refers to the stickiness or adhesive properties of a material.Non-tacky refers to a material that does not possess any degree ofstickiness or adhesive properties, whereas tacky materials possess somedegree of stickiness or adhesive properties. Non-tacky materials maypossess a high coefficient of friction, therefore also making non-tackymaterials useful as non-slip coatings.

If the non-slip coating is tacky, it is desirable that it have a lowlevel of tackiness. By low level of tackiness, it is meant that thenon-slip coating has an average tack level, as measured by ASTM D2979-01(Standard Test Method for Tack of Pressure-Sensitive Adhesives Using anInverted Probe Machine) using a ten (10) second dwell time, and a proberemoval speed of one (1) cm/s, of no greater than about 200 grams, nogreater than about 250 grams, no greater than about 300 grams, and nogreater than about 350 grams. It is desirable that the material used toform the non-slip coating layer 14 bond directly to the backing layer12. If the non-slip material does not form an effective bond with thebacking layer, the backing layer 12 may be primed to allow the non-slipmaterial to form a more effective bond with the backing layer 12.

In one embodiment, the non-slip coating 14 is slightly tacky, and has anadhesion to itself that is less than the cohesive strength of thenon-slip coating itself, and further has an adhesion to itself that isless than the “two-bond” adhesive strength. As is known to those skilledin the art, the “two-bond” adhesive strength is the adhesive strengthbetween the non-slip coating 14 and the backing layer 12 to which thenon-slip coating layer is applied. Thus, when the non-slip coating 14 isfolded over onto itself, the respective non-slip surfaces that come intocontact can be released again without experiencing cohesive failure ofthe non-slip layers, and without having the non-slip layer 14 detachingfrom the backing layer 12.

In another aspect, the non-slip coating provides a surface that may berepeatably bonded to itself. In another somewhat related aspect, thenon-slip coating 14 may be repositionable. As used herein,“repositionable” refers to a non-slip coating that allows repeatedapplication, removal, and reapplication to and from itself or a surfacewithout damage to the non-slip coating or the surface.

In addition, it is desirable that the adhesion of the non-slip coatinglayer 14 to itself not build significantly over time. As such, if theabrasive article 10 is folded over onto itself such that the non-slipcoating layer 14 contacts itself, the abrasive article 10 may later bereadily unfolded by separating the non-slip coating layers 14 withoutdamaging the non-slip coating 14 or the backing layer 12.

Suitable materials for the non-slip coating layer 14 include, forexample, elastomers. Suitable elastomers include: natural and syntheticrubbers such as synthetic polyisoprene, butyl rubbers, polybutadiene,styrene-butadiene rubber (SBR), block copolymers such as Kraton rubber,polystyrene-polyisoprene-polystyrene (SIS) rubber,styrene-butadiene-styrene (SBS) rubber, nitrile rubber (Buna-N rubbers),hydrogenated nitrile rubbers, acrylonitrile butadiene rubber (NBR),chloroprene rubber, polychloroprene, neoprene, EPM rubber (ethylenepropylene rubber), EPDM rubber (ethylene propylene diene rubber),acrylic rubber, polyacrylic rubber, silicone rubber, ethylene-vinylacetate (EVA), polyvinyl acetate (PVA), and other types of elastomerssuch as thermoplastic elastomers, thermoplastic vulcanizates such asSantoprene thermoplastic rubber, urethanes such as thermoplasticpolyurethane, and thermoplastic olefins.

Such rubber materials may further include a tackifying agent. Exemplarytackifiers include, for example, C5 and C9 tackifiers. Exemplarycommercially available tackifiers include Wingtack type tackifierresins, available from TOTAL Cray Valley, Exton, Pa.

The non-slip coatings of the present disclosure further include a dimeracid polyamide. In some embodiments, the dimer acid polyamide assists inproviding heat resistance to the non-slip coating or layer. Dimer acidscan be obtained by the polymerization of C18-acids such as oleic andlinoleic acids, and are often environmentally friendly chemical reagentswith characteristics of being biodegradable. Polyamides can be preparedby melt-polycondensation reactions using dimer acids and differentdiamines as raw materials. The dimer acid-based polyamides synthesizedpossess advantages of being soluble in many solvents, biodegradable,flexible and demonstrating good hot melt adhesion. Formulations andsynthesis techniques of dimer acid-based polyamides can be found, forexample, in U.S. Pat. No. 3,377,303 (Peerman et al.) U.S. Pat. No.3,483,237 (Peerman et al.); U.S. Pat. No. 5,085,099 (Jaeger); U.S. Pat.No. 5,138,027 (Van Beek); and U.S. Pat. No. 5,455,326 (Parker)

In some embodiments, the non-slip coating or layer includes betweenabout 20% and about 55% by weight of dimer acid polyamide. In someembodiments, the non-slip coating or layer includes between about 25%and about 50% by weight of dimer acid polyamide. In some embodiments,the non-slip coating or layer includes between about 30% and about 45%by weight of dimer acid polyamide. In some embodiments, the non-slipcoating or layer includes greater than about 20% by weight of dimer acidpolyamide or greater than about 25% by weight of dimer acid polyamide,or greater than about 30% by weight of dimer acid polyamide, or greaterthan about 35% by weight of dimer acid polyamide, or greater than about40% by weight of dimer acid polyamide. In some embodiments, the non-slipcoating or layer includes less than about 55% by weight of dimer acidpolyamide or less than about 50% by weight of dimer acid polyamide orless than about 45% by weight of dimer acid polyamide or less than about40% by weight of dimer acid polyamide or less than about 35% by weightof dimer acid polyamide.

In some embodiments, the dimer acid polyamide is present in a ratio ofbetween about 70:16 and about 31:55 (dimer acid polyamide: SIS blockcopolymer). Exemplary commercially available dimer acid polyamidesinclude UNIREZ resins, available from Kraton Corporation, Houston, Tex.

In some instances, the non-slip coating on the sandpaper may soften ormelt and stick to the power tools, and potentially ruining the powertool. It is desirable that the coating have a low hot melt adhesion toaddress this issue without significantly compromising the advantages ofa non-slip sandpaper. To this end, a test method was developed tomeasure the relative hot melt adhesion of compounded formulations to asteel surface. Please see the Relative Hot-Melt Adhesion Test Methoddescription below. It is desirable that the relative hot-melt adhesion(according to this test method) generate an axial force at 80° C. below−18 Newtons, preferably in the range −15 Newtons to −5 Newtons.

The tackiness of such elastomeric non-slip coating layers may beadjusted by adding fillers, such as calcium carbonate, to the material.

In one aspect, the non-slip coating layer may have a glass transitiontemperature of at least about −80 degrees Celsius (° C.), at least about−70° C., and at least about −65° C., and a glass transition temperatureof no greater than about −5° C., no greater than about −15° C., and nogreater than about −25° C. In a more specific aspect, the non-slipcoating layer 14 is formed of an aqueous solution that forms a coatinglayer having a glass transition temperature of at least about −80degrees Celsius (° C.), at least about −70° C., and at least about −65°C., and a glass transition temperature of no greater than about −5° C.,no greater than about −15° C., and no greater than about −25° C.

Commercially available materials suitable for producing elastomericnon-slip coating layers include Butofan NS209, a carboxylatedstyrene-butadiene anionic dispersion available from BASF Corporation,Florham Park, N.J., and Hystretch elastomeric dispersions V-29, V-43,and V-60 available from Lubrizol Corporation, Wickliffe, Ohio.Ethylene-vinyl acetate (EVA) dispersions may also be used.

Suitable materials for producing the non-slip coating layer 14 alsoinclude acrylates and acrylic polymers. In addition, suitable materialsfor producing the non-slip coating layer 14 include pressure sensitiveadhesives, such as acrylic adhesives—which may or may not include a tackmodifying ingredient—repositionable adhesives, or hot melt acrylicadhesives. Depending on the particular composition, and depending on thedegree of processing (for example, the degree of polymerization), suchhot melt acrylic adhesives can be produced with a variety of physicalcharacteristics including both tacky and non-tacky characteristics.

The particular thickness of the non-slip coating layer 14 may varydepending on, for example, the material selected to form the non-slipcoating layer 14, and depending on the intended end use application forthe abrasive article 10. For example, a non-slip coating layer 14 formedof rubber or urethane base material may have a thickness of at leastabout 0.1 mil (2.5 micrometers), at least about 1 mil (25 micrometers),and at least about 10 mils (254 micrometers), and a thickness of nogreater than about 50 mils (1270 micrometers), no greater than about 30mils (762 micrometers), and no greater than about 25 mils (635micrometers). A non-slip coating layer 14 formed of an acrylic polymercoating, on the other hand, may be thinner, and may have a thickness ofat least about 0.1 (2.5 micrometers), at least about 0.5 (12.7micrometers), and at least about 1 mil (25.4 micrometers), and athickness of no greater than about 2 mils (50.8 micrometers), no greaterthan about 5 mils (127 micrometers), and no greater than about 10 mils(254 micrometers).

A non-slip coating layer 14 formed from a dried styrene-butadiene rubberdispersion or a dried latex dispersion may have a coating weight of atleast about 1 gram/square meter (g/m²) (0.24 grains/24 square inch(grains/24 in²)), at least about 3 g/m² (0.72 grains/24 in²), or atleast about 4 g/m² (0.96 grains/24 in²), and a coating weight of nogreater than about 20 g/m² (4.8 grains/24 in²), no greater than about 15g/m² (3.6 grains/24 in²), or no greater than about 12 g/m² (2.9grains/24in²).

In one embodiment, a suitable non-slip coating layer 14 may be producedusing a pressure sensitive adhesive by coating a polymerizable pressuresensitive adhesive composition onto the backing layer 12, and thenpolymerizing the pressure sensitive adhesive composition to produce anon-slip coating layer having the desired properties, or by coating arepositionable pressure sensitive adhesive onto the backing layer 12.

In a specific embodiment, the pressure sensitive adhesive is an acrylichot melt adhesive that may be produced by, for example, providing apolymerizable liquid monomer mixture in a sealed pouch formed of, forexample, ethylene vinyl acetate (EVA), at least partially polymerizingthe liquid monomer mixture by, for example, exposing the liquid monomermixture to actinic radiation (e.g., ultraviolet light), blending thepartially polymerized liquid with the EVA material used to form thepouch, thereby forming a coatable pressure sensitive adhesivecomposition, and coating the pressure sensitive adhesive compositiononto a backing layer 12. After the pressure sensitive adhesivecomposition has been coated onto the backing layer 12, the non-sliplayer 14 is formed by further polymerizing the pressure sensitiveadhesive to form a non-slip coating layer having the desiredcharacteristics, such as a coating layer having a low level of tack, orno tack.

The degree of additional polymerization may vary, and will depend, forexample, on the desired properties of the non-slip layer 14. Furtherpolymerization may be accomplished by, for example, exposing thepressure sensitive adhesive to additional UV light or by thermalpolymerization in an amount sufficient to reduce the level of tack ofthe pressure sensitive adhesive to the desired level.

A suitable polymerizable liquid monomer mixture may include, forexample, a mixture of 2 ethyl hexyl acrylate, butyl acrylate, methylacrylate, and a photo-initiator such as Irgacure 651 available fromCiba-Geigy Corp. Hawthorne, N.Y. Optional additives such as isooctylthioglycolate, hexanediol diacrylate, alphabenzophenone, and Irganox1076 antioxidant available from Ciba Specialty Chemicals Corporation,Tarrytown, N.Y., may also be included in the polymerizable liquidmonomer mixture.

In some embodiments, the non-slip coating layer 14 can be applied as aliquid suspension, such as an aqueous dispersion, an aqueous emulsionsuch as a latex, or as a hot melt adhesive.

Liquids may be applied using a variety of known printing and/or coatingtechniques including, for example, roll coating (e.g., rotogravurecoating), transfer roll coating, solvent coating, hot melt coating,spray coating, Meyer rod coating, and drop die coating. Particularlydesirable techniques for applying aqueous emulsions and dispersionsinclude Meyer rod coating, rotogravure and transfer roll coatingtechniques. Such aqueous emulsions and dispersions are then allowed todry to produce the non-slip coating layer 14. A particularly desirabletechnique for applying a hot melt adhesive, such as an acrylate hot meltadhesive, is drop die coating. Such a hot melt coated adhesive is thenfurther polymerized to produce a non-slip coating layer 14 having thedesired characteristics.

In one embodiment, the non-slip coating layer 14 is provided with asurface texture. Such a textured surface may be provided by applying theliquid emulsion or liquid dispersion to the backing layer 12 using, forexample, a microcell foam roller or through spray coating. In aparticular embodiment, a liquid emulsion or liquid dispersion is appliedusing a microcell foam roller to a coating weight of about 3 grains/24square inch. The liquid coating may then be dried, for example, in aforced air oven at a temperature of 225 degrees Fahrenheit for 5 minutesto produce the non-slip coating layer.

In the embodiment illustrated in FIG. 1, the non-slip coating 14 definesa generally planer outer surface 14 a of the sandpaper 10 opposite themake coat 16 and abrasive particles 18. That is, the non-slip coatinglayer 14 defines a smooth outer surface that does not include a texturedsurface or a macroscopic three dimensional surface topography. Thecoating layer 14 may be continuous, discontinuous, and/or applied inrandom or repeating patterns, such as dots and stripes.

In some embodiments, the non-slip coating layer 14 may be clear. In thismanner, any information or indicia printed on the backing 12 will remainvisible through the non-slip coating layer 14. In addition, theappearance of the sandpaper remains similar to the appearance ofconventional sandpaper, to which users have become accustomed.

As illustrated in FIG. 2, the outer surface 14 a of the non-slip coatinglayer 14 may include a regular patterned surface texture or geometry. Inthe specific embodiment illustrated, the patterned surface texture ofthe non-slip coating layer 14 outer surface 14 a may be such that thepattern inter-engages with itself when the sandpaper 10 of folded overonto itself. That is, the outer surface 14 a includes raised 14 a′ andrecessed 14 a″ regions that mate with each other when the outer surface14 a is folded over onto itself.

In either of the embodiments shown in FIG. 1 or 2, the non-slip coatinglayer 14 may further comprise filler material or particles to providethe non-slip coating layer 14 outer surface 14 a with a rough orrandomly textured surface. Such a rough or textured surface serves toenhance the traction properties of the non-slip coating layer 14.

Make Coat 16

In general, any adhesive make coat 16 may be used to adhere the abrasiveparticles 18 to the backing layer 12. “Make coat” refers to the layer ofhardened resin over the backing layer 12 of the sandpaper 10. Suitablematerials for the adhesive make coat 16 include, for example, phenolicresins, aminoplast resins having pendant α,β-unsaturated carbonylgroups, urethane resins, epoxy resins, ethylenically unsaturated resins,acrylated isocyanurate resins, urea-formaldehyde resins, isocyanurateresins, acrylated urethane resins, acrylated epoxy resins, bismaleimideresins, fluorene-modified epoxy resins, and combinations thereof.

The make coat 16 may be coated onto the backing layer 12 by anyconventional technique, such as knife coating, spray coating, rollcoating, rotogravure coating, curtain coating, and the like. Thesandpaper 10 may also include an optional size coat (not shown).

Abrasive Particles 18

In general, any abrasive particles 18 may be used with this disclosure.Suitable abrasive particles include, for example, fused aluminum oxide,heat treated aluminum oxide, alumina-based ceramics, silicon carbide,zirconia, alumina-zirconia, garnet, emery, diamond, ceria, cubic boronnitride, ground glass, quartz, titanium diboride, sol gel abrasives andcombinations thereof The abrasive particles 18 can be either shaped(e.g., rod, triangle, or pyramid) or unshaped (i.e., irregular). Theterm “abrasive particle” encompasses abrasive grains, agglomerates, ormulti-grain abrasive granules. The abrasive particles can be depositedonto the make coat 16 by any conventional technique such aselectrostatic coating or drop coating.

Additives

The make coat 16 and/or the optional size coat may contain optionaladditives, such as fillers, fibers, lubricants, grinding aids, wettingagents, thickening agents, anti-loading agents, surfactants, pigments,dyes, coupling agents, photo-initiators, plasticizers, suspendingagents, antistatic agents, and the like. Possible fillers includecalcium carbonate, calcium oxide, calcium metasilicate, aluminatrihydrate, cryolite, magnesia, kaolin, quartz, and glass. Fillers thatcan function as grinding aids include cryolite, potassium fluoroborate,feldspar, and sulfur. The amounts of these materials are selected toprovide the properties desired, as is known to those skilled in the art.

In a specific embodiment, the sandpaper 10 is a standard 9×11 inch sheetof sandpaper. In other embodiments, the sandpaper 10 may have a width ofabout 3 to about 4 inches, or of about 5 to about 6 inches, and a lengthof about 8 to about 10 inches, or about 10 to about 12 inches.

In another aspect, the present disclosure provides a package ofsandpaper including a stack of sheets of sandpaper. The stack mayinclude at least 2 sheets, at least about 6 sheets, or at least about 10sheets.

Methods of Making

The various embodiments described above may be made using a variety oftechniques, and will vary depending on the particular material used toproduce the non-slip coating layer 14. For example, the abrasive article10 may be made by providing a paper backing layer, coating an adhesivemake coat on one major surface of the backing layer, at least partiallyembedding abrasive particles in the make coat, thereby forming anabrasive surface, dissolving a non-slip coating material, such as amixture of rubber and tackifier, in a hydrocarbon solvent, such astoluene, thereby to form a coatable non-slip material, coating thenon-slip material and solvent onto the surface of the backing layeropposite the make coat, and allowing the solvent to evaporate from thenon-slip material, thereby forming a non-slip coating layer 14 on thebacking layer 12. Using this technique, the non-slip coating layer 14 issaid to be “solvent coated” onto the backing.

In another method of making the abrasive article 10, an aqueous emulsionor aqueous dispersion is coated onto the backing layer 12 opposite themake coat 16, and is dried, thereby forming the non-slip coating layer14.

Alternatively, the abrasive article 10 may be made by providing a paperbacking layer 12, coating an adhesive make coat 16 on one major surfaceof the backing layer 12, at least partially embedding abrasive particles18 in the adhesive make coat 16, thereby forming an abrasive surface,providing a non-slip material such as a mixture of rubber and tackifier,heating the non-slip material, thereby forming a coatable non-slipmaterial, and coating the non-slip material onto the surface of thebacking layer 12 opposite the make coat 16, thereby forming a non-slipcoating layer 14. With this technique, the non-slip coating layer 14 maybe coated onto the backing layer 12 using, for example, roll coating,hot melt coating, or drop die coating techniques.

In one embodiment, the roller used to apply the coatable non-slipmaterial is a foam roller, which imparts a surface texture to thenon-slip coating layer. Alternatively, a foam roller may be used to posttreat the non-slip coating layer 14 after it has been coated onto thebacking layer 12, thereby imparting the non-slip coating layer with asurface texture.

In another method of making the abrasive article 10, an adhesive, suchas an acrylic hot melt adhesive, is coated onto the backing layer 12opposite the make coat 16, and is cured by, for example, polymerizationor drying, thereby forming the non-slip coating layer 14.

In any of the above techniques, it will be recognized that the order inwhich the non-slip coating layer 14 and made coat layer 16 are appliedto the backing layer 12 may be varied. That is, the non-slip coatinglayer 14 may be applied to the backing layer 12 either before or afterthe make coat 16 is applied to the backing layer 12.

In addition, it will be recognized that the backing layer 12, make coat16, and abrasive particles 18 may be provided in the form of apre-formed (i.e., otherwise complete) abrasive sheet. That is, ratherthan providing a backing layer 12, which is then coated with make coat16 and provided with abrasive particles 18 to form an abrasive sheet, apre-formed abrasive sheet including a backing, make coat and abrasiveparticles may be provided. The non-slip coating layer 14 can then beapplied directly to the pre-formed abrasive sheet.

Representative examples of suitable pre-formed abrasive sheets areavailable under the product designation 216U, from 3M Company, St. Paul,Minn. 216U is sandpaper having an A weight backing, a phenolic makecoat, aluminum oxide abrasive particles, and a stearic acid supersizecoating, which is provided to minimize loading. If a pre-formed abrasivesheet is used, the non-slip coating layer 14 may be applied to thebacking layer 12 using, for example, solvent coating, roll coating, hotmelt coating, drop die, or powder coating techniques. For ease ofmanufacturing, it is desirable to provide the finished sandpaper in bulkform, and then coat the bulk sandpaper with the non-slip coatingmaterial prior to producing the individual sheets of sandpaper that areultimately used by the end user.

A wide variety of commercially available conventional sandpaperconstructions having a wide variety of backing materials (e.g., papers,films, cloths), weights (e.g., A, B, or C weight paper), and abrasiveparticles may be coated with a non-slip coating according to the presentdisclosure.

Surprising, the abrasive articles including the non-slip coating layerof the present disclosure display superior resistance to curling whenimmersed in water or subjected to humid environments. When tested inaccordance with the Wet Curl test (described in the Examples sectionbelow), the abrasive articles preferably do not substantially curl.

In order that the disclosure described herein can be more fullyunderstood, the following examples are set forth. It should beunderstood that these examples are for illustrative purposes only, andare not to be construed as limiting this disclosure in any manner.

EXAMPLES Materials

-   PRODAS 2075, a poly alpha olefin based hot melt adhesive resin,    available from Beardow Adams, Bradville, Milton Keynes, England.-   3M SCOTCHWELD 3789, a polyamide hot-melt adhesive, is available from    3M Company, St. Paul Minn. HJ-H2060 polyamide is available from    Shandong Huijin Chemical Co., Ltd. (Daozhuang, Guangrao, Dongying    City, Shandong Province, China)-   UNIREZ 2626, a hot-melt polyamide, is available from Kraton    Corporation, Houston, Tex.-   UNIREZ 2720, a hot-melt polyamide, is available from Kraton    Corporation, Houston, Tex.-   KRATON D1161, a styrene-isoprene-styrene block copolymer, is    available from Kraton Corporation, Houston, Tex.-   WINGTACK PLUS, a C-5 tackifier resin, is available from TOTAL Cray    Valley, Exton.

Relative Hot Melt Adhesion Test (Axial Force)

Samples for this test method were prepared using a Type Six melt mixerwith CAM blades from Brabender Instruments, Inc., South Hackensack, N.J.The melt mixer was heated to 180° C. and the CAM blades were set to mixat a rate of 65 rpm. Ingredients were added in the relative amountsdescribed for the non-slip coating formulations in Table 1 to providesample sizes of approximately 60 grams. After the contents were visuallywell mixed, usually lasting a period from 2-3 minutes, the mixture wasthen drained from the mixing bowl into an aluminum tray for analysis.

Analysis was performed using a Discovery Hybrid Rheometer HR-2 from TAInstruments, New Castle, Del. About 3 grams of test material (non-slipformulation) was melted and set between two circular parallel steelplates of the rheometer at a gap of 0.8 mm. The top plate measured 20 mmin diameter while the bottom plate measured 100 mm in diameter. Thebottom plate was a Peltier temperature controlled plate that performed atemperature sweep from 190° C. to 80° C. in steps of 10° C. with anequilibrium of 60 seconds at each temperature step. The top platesubjected each sample to a fixed 1.25% small amplitude oscillatorystrain at a constant frequency of 10 Hz. As each sample cools whiletraveling through the temperature regime, it contracts and exerts anaxial force that pulls on the top plate of the rheometer. The magnitudeof the axial force is proportional to the relative adhesion of thenon-slip coating material to the top plate and is measured by a forcetransducer attached to the top plate of the rheometer and recorded.

Dry Coefficient of Friction Test

Coefficient of Friction is measured according to ASTM D 1894-08.

Wet Coefficient of Friction Test

Samples for this test method are placed in water under ambientconditions in a tin pan (approx. 1 inch of water) and soaked forapproximately 5 minutes. Samples are promptly removed and theCoefficient of Friction is measured according to ASTM D 1894-08.

Tack Test

Tack is measured according to Probe Tack Test ASTM 2979-01.

Wet Curl Test

Samples for this test method are provided or cut into 3 inch by 6 inchstrips. Samples are placed in water under ambient conditions in a tinpan (approx. 1 inch of water) and soaked for approximately 5 minutes.Samples are visually inspected for curling while still in water. As usedin reference to this test method, a sample does not substantially curlif the opposing ends are not drawn towards one another such that; a)neither of the opposing end edges reaches a location adjacent the centerof the strip; and/or b) the opposing ends of the strip are generallycoplanar.

Examples E1-E8 and Comparative Examples CE1-CE4

The non-slip formulations in Table 1 were all prepared by a melt mixingprocess, conducted on an 18 mm Berstoff Twin screw extruder(KraussMaffei Technologies GmbH, Munich, Germany). The extrudate fromthe extruder was then coated on to 216U P150 sandpaper, available fromby 3M Company, St. Paul, Minn. 216U P150 sandpaper is a general purposesandpaper having an A-weight paper backing, a phenolic resin coated onone side, and aluminum oxide abrasive particles at least partiallyembedded on the phenolic resin. The second side (i.e., the non-abrasiveside opposite the abrasive surface) of the sandpaper was then coatedwith one of the non-slip coating formulations to a thickness of about4-5 mils. The Dry Coefficient of Friction and Tack for the non-slipcoatings of Examples E1-E8 were measured. As a control, the DryCoefficient of Friction and Tack was also measured for 3M 216U P150sandpaper. Dry Coefficient of Friction was also measured for ComparativeExamples CE1-CE4. The results are summarized in Table 2.

TABLE 1 KRATON 1161D HJ-H2060 SIS block copolymer polyamide WINGTACKPLUS Example (wt %) (wt %) tackifier resin (wt %) E1 16 59 25 E2 35 4520 E3 25 52 23 E4 26 57 17 E5 45 33 22 E6 35 51 14 E7 55 31 14 E8 16 7014

TABLE 2 Static Kinetic Coefficient of Coefficient of Probe ExampleFriction Friction Tack (grams) E1 1.238 1.234 0 E2 3.384 2.187 27  E35.692 1.674 0 E4 3.660 1.884 0 E5 5.943 3.157 0 E6 2.962 2.587 0 E75.471 2.898 0 E8 3.331 3.124 0 CE1 (UNIREZ 2720) 0.584 1.100 Notmeasured CE2 (UNIREZ 2626) 0.252 0.777 Not measured CE3 (SCOTCHWELD2.938 2.790 Not measured 3789) CE4 (PRODAS 2075) 1.731 2.605 Notmeasured Control (3M 216U 0.268 0.189 0 P150 sandpaper)

The Relative Hot Melt Adhesion was measured for the non-slipformulations of Examples E6, E7, E9 and the Comparative Examples CE1-CE4using the Relative Hot Melt Adhesion test method described above. Theevolution of this axial force for the samples tested is summarized inTable 3. The negative sign of the force is in reference to its directionas a compressive force, i.e., meaning exerting a pull on the top plate.The 80° C. is a relevant temperature because the non-slip coatings onthe sandpaper typically will soften or melt and stick to power toolsaround that that temperature. The less pull exerted (lower negativenumber) is an indication that there would be relatively low or noadhesion to a power tool surface.

TABLE 3 Axial Force (Newtons) Temper- CE1 CE2 CE3 CE4 ature (UNIREZ(UNIREZ (SCOTCH- (PRODAS (° C.) E6 E7 E8 2720) 2626) WELD 3789) 2075)190 0.01 0.20 0.02 0.01 0.09 0.03 0.02 180 0.00 0.13 0.00 0.01 0.28 0.030.01 170 0.00 0.06 0.00 0.01 1.15 0.03 0.02 160 −0.01 −0.07 −0.01 0.010.51 0.03 0.01 150 −0.01 −0.22 −0.01 0.01 −5.16 0.03 −0.01 140 0.00−0.45 −0.01 0.01 −14.14 0.02 0.00 130 −0.03 −0.76 −0.03 0.01 −25.83 0.020.00 120 −0.03 −1.21 −0.02 0.01 0.01 −1.50 110 −0.06 −2.13 −0.07 0.01−0.06 −10.66 100 −0.14 −3.65 −0.13 0.01 −0.56 −20.68 90 −1.01 −6.05−0.51 −3.35 −6.21 −27.04 80 −12.48 −10.88 −5.49 −21.24 −18.24 −32.45

Examples E9-E12

To construct Examples E9-E12, the second, non-abrasive side of 431Qsandpaper, available from by 3M Company, St. Paul, Minn., was coatedwith the non-slip coating formulation of Example E6 (prepared as above)to a thickness of about 4-5 mils. 431Q sandpaper is a general-purposesandpaper having a C-weight paper backing, a phenolic resin coated onone side, and silicon carbide abrasive particles at least partiallyembedded in the phenolic resin. Examples E9-E10 feature 431Q, P240sandpaper, while Examples E11-E12 feature 431Q, P600 sandpaper. The DryCoefficient of Friction for the non-slip coatings of Examples E9 and E11were measured. The Wet Coefficient of Friction for the non-slip coatingsof Examples E10 and E12 were measured. The Dry and Wet Coefficient ofFriction was also measured for Comparative Example CE5 and CE6,respectively. The results are summarized in Table 4.

TABLE 4 Static Coefficient of Kinetic Coefficient of Example FrictionFriction E9 2.211 2.292 E10 1.793 1.883 E11 2.243 2.498 E12 2.176 2.360CE5 (SANDWET, 0.241 0.112 P400) CE6 (SANDWET, 0.856 0.812 P400)

Example 13

To construct example E13, the second, non-abrasive side of 413Q, P400sandpaper, available from by 3M Company, St. Paul, Minn., was coatedwith the non-slip coating formulation of Example E6 to a thickness ofabout 4-5 mils. 413Q sandpaper is a general-purpose sandpaper having anA-weight paper backing, a phenolic resin coated on one side, and siliconcarbide abrasive particles at least partially embedded in the phenolicresin. A GATOR brand P320 waterproof sanding sheet and 413Q, P400sandpaper served as Comparative Examples CE7 and CE8, respectively.

The Wet Curl was evaluated for E13, CE7, and CE8 using the Wet Curl testmethod described above. The results for the tested samples are depictedin FIG. 3.

The patents, patent documents, and patent applications cited herein areincorporated by reference in their entirety as if each were individuallyincorporated by reference. It will be apparent to those of ordinaryskill in the art that various changes and modifications may be madewithout deviating from the inventing concepts set from above. Thus, thescope of the present disclosure should not be limited to the structuresdescribed herein. Those having skill in the art will appreciate thatmany changes may be made to the details of the above-describedembodiments and implementations without departing from the underlyingprinciples thereof. Further, various modifications and alterations ofthe present disclosure will become apparent to those skilled in the artwithout departing from the spirit and scope of the invention. The scopeof the present application should, therefore, be determined only by thefollowing claims and equivalents thereof.

1. Sandpaper, comprising: a backing layer having opposed first and second major surfaces; an adhesive make coat directly on the first major surface; abrasive particles at least partially embedded in the make coat, thereby defining an abrasive surface; and a non-slip layer on the second major surface, the non-slip layer comprising: a dimer acid polyamide; an elastomer; and a tackifying agent.
 2. The sandpaper of claim 1, wherein the elastomer is selected from the group consisting of natural rubber, synthetic rubber, ethylene-vinyl acetate (EVA), polyvinyl acetate (PVA), thermoplastic vulcanizates, acrylates, acrylic polymers, thermoplastic olefins and combinations thereof.
 3. The sandpaper of claim 2, wherein the elastomer is synthetic rubber, and wherein the synthetic rubber is selected from the group consisting of styrene-butadiene rubber (SBR), polystyrene-polyisoprene-polystyrene (SIS) rubber, polyisoprene, ethylene-propylene terpolymers (EPDM rubber), silicone rubber, and polyurethane rubber.
 4. The sandpaper of claim 1, wherein the non-slip layer includes between about 10% and about 60% by weight of a styrene-isoprene-styrene block copolymer.
 5. The sandpaper of claim 1, wherein the non-slip layer includes between about 15% and about 75% by weight of a dimer acid polyamide.
 6. The sandpaper of claim 1, wherein the ratio of dimer acid polyamide to styrene-isoprene-styrene block copolymer is between about 70:16 to about 31:55.
 7. The sandpaper of claim 1, wherein the non-slip layer includes between about 10% and about 25% by weight of tackifying agent.
 8. The sandpaper of claim 1, wherein the tackifying agent is a C5 or C9 tackifier resin.
 9. The sandpaper of claim 1, wherein the non-slip coating layer is non-tacky.
 10. The sandpaper of claim 1, wherein the non-slip coating layer has an average tack level, as measured by ASTM D2979-01 using a 10 second dwell time, and a probe removal speed of 1 cm/s of no greater than about 300 grams.
 11. The sandpaper of claim 1, wherein the non-slip coating layer is configured to selectively fold over onto itself, bond to itself, and release from itself such that, when bonded to itself, the non-slip coating layer has an adhesion that is less than a two-bond adhesion of the non-slip coating layer to the backing layer, whereby the non-slip coating layer does not separate from the backing layer when the non-slip coating layer is separated from itself.
 12. The sandpaper of claim 1, wherein the non-slip coating layer has a thickness of between at least about 0.2 mils and no greater than about 50 mils.
 13. The sandpaper of claim 1, wherein the non-slip coating layer has a coating weight of at least about 4 g/m² and no greater than about 20 g/m².
 14. The sandpaper of claim 1, wherein the non-slip coating layer comprises a continuous uniform outer surface opposite the abrasive particles.
 15. The sandpaper of claim 1, wherein the non-slip coating layer has an average peak static coefficient of friction of at least about 1 gram when measured according to ASTM D 1894-08.
 16. The sandpaper of claim 1, wherein the non-slip coating layer has an average kinetic coefficient of friction of at least about 0.75 grams when measured according to ASTM D 1894-08.
 17. The sandpaper of claim 1, wherein the relative hot-melt adhesion of the non-slip coating layer generates an axial force of −18 Newtons, preferably in the range −15 Newtons to −5 Newtons, at 80° C.
 18. The sandpaper of claim 1, wherein the non-slip layer having a rough or randomly textured surface and configured to selectively fold over onto itself, bond to itself, and release from itself such that, when bonded to itself, the non-slip coating layer has an adhesion level that is less than a cohesive strength of the non-slip coating layer, whereby the non-slip coating layer is not damaged when the non-slip coating layer is separated from itself. 